[Zeke]

There are lot of gimmicks to reattach loose plaster and strip lath to the joists. That's the first step. Then, dig out the cracks and fill with expanding patch (used to be called FixAll, Fix-it-All may be the same). Let dry for a few days and sand those seems and other nasty areas, roughing them up. Then, use an oil based undercoater to seal the whole area. After that, you can redo the ceiling with drywall mud; the all purpose or taping compound, not topping.

Around here, some rip the walls down and leave the ceilings. The reason for this is as mentioned, new wiring and insulation. The ceilings are insulated easily from the attic, as you know.

I could go on and on as I've been doing this kind of work off and on for 35 years. I just want to say that if you take down the exterior, the hammering, etc. will pretty much mess up what you have left for inside walls. The only drawback is that you can't get a continuous moisture wrap on the outside. The moisture barrier side of the insulation faces inward leaving the insulation to get wet and freeze. Hopefully your exterior is tight.